Field of the Invention
The present invention relates to electronics and, more specifically, to voltage-controlled oscillators.
Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Voltage-controlled oscillators (VCOs) are widely used in the semiconductor industry, such as in transceivers for clock and data recovery (CDR) circuits and phase-locked loop (PLL) circuits. It is desirable for VCOs to have a wide tunable frequency range, for example, to support various communication protocols, while still maintaining low power, low noise, and low supply sensitivity.
A conventional VCO has a tunable output frequency that is a function of an input voltage or current. High-frequency VCOs that traditionally satisfy the low noise/jitter criteria specified by communication protocols are either power hungry or support only a narrow band of frequencies. For example, LC-tank VCOs can yield relatively low phase noise at high frequency, but have a narrow frequency range. On the other hand, high-frequency, wideband ring VCOs are power hungry and have difficulty meeting jitter budgets. In addition, ring VCOs characteristically have a dedicated, opamp-based regulator in order to provide low supply sensitivity, which further increases VCO power consumption.